1. Field of the Invention
The present invention relates to the field of liquid crystal display, and in particular to a method for manufacturing a photo mask for vapor deposition of organic light-emitting display panel and a photo mask manufactured with the method.
2. The Related Arts
Flat panel display devices have a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and are thus widely used. The flat panel display devices that are currently available include liquid crystal displays (LCDs) and organic light-emitting displays (OLEDs).
Referring to FIG. 1, a currently available organic light-emitting display generally comprises: a glass substrate 900, a transparent conductive layer 902 formed on the glass substrate 900, a hole transporting layer (HTL) 904 formed on the transparent conductive layer 902, an organic emitting material layer (EML) 906 formed on the hole transporting layer 904, and an electron transporting layer (ETL) 908 formed on the organic emitting material layer 906, and a cathode 909 formed on the electron transporting layer 908, in which the transparent conductive layer 902 serves as an anode of the organic light-emitting display and is generally made of indium tin oxide (ITO). When the organic light-emitting display is subjected to a forward bias caused by a direct current, the energy of the externally applied voltage drives electrons and holes to inject into the organic light-emitting display from the cathode 909 and the anode 902 respectively. When the electrons and the holes meet and re-combine with each other during transportation, the so-called “electron-hole capture” occurs. When the chemical molecules of the organic emitting material layer 906 are excited by the external energy, if the electron spin thereof is paired with the ground state electron, then it is referred to as “singlet” and light released therefrom is fluorescence; and if the excited electron and the ground state electron are of electron spins that are not paired and are parallel to each other, then it is referred to as “triplet” and the light released therefrom is phosphorescence. When the state of an electron goes from an excited, high energy state back to a stable, low energy state, energy will be released in the form of light emission or heat dissipation, of which some of the photons are used for the function of displaying.
In a manufacturing process of an organic light-emitting display, vapor deposition is commonly adopted, wherein vapor-deposited area is defined by arranging vapor deposition apertures in photo masks that correspond to predetermined patterns to be formed in the layers, whereby desired patterns can be formed on the substrate.
Vapor deposition is often carried out in a vacuum chamber with a bottom surface of a substrate serving as a deposition surface. A photo mask is placed between the deposition surface and a vapor source. To carry out vapor deposition, the vapor source is heated to evaporate a deposition material to allow the material to pass through the vapor deposition apertures of the photo mask and attach to the deposition surface thereby forming a desired pattern on the deposition surface.
Referring to FIG. 2, a schematic view of the structure of a conventional photo mask is shown, which is generally made of a material, such as glass, quartz, magnesium fluoride, and calcium fluoride, of which the thermal expansion coefficient is identical or less than that of a processed substrate and comprises a plurality of working units 11 arranged in an array. In a working unit 11, a shielding layer 12 of which the thickness is around 50-500 μm is formed through inwards recessing and the shielding layer 12 is provided with through apertures that are formed to correspond to a predetermined pattern to serve as vapor deposition apertures 13. To prevent the working unit 11 from deformation that leads to deviation of preciseness of deposition, the working unit 11 is provided, along a perimeter thereof, with a rib 14 that has a greater thickness of approximately 50 μm to several centimeters. To use, the photo mask is retained under the deposition surface of the processed substrate by a support mechanism (not shown). However, since it is thin, it is difficult to position and fix, the installation being more time-consuming and the manufacture cost being relatively high.
To overcome the above-discussed problem, a photo mask that is made of a magnetic material and can be attracted and fixed by magnetism. As shown in FIGS. 3 and 4, the photo mask is provided with a plurality of effective open areas 100 and ineffective areas 300 between the effective open areas 100. The effective open areas 100 are provided with vapor deposition apertures (not shown) formed thereon to correspond to a predetermined pattern. Before the conduction of vapor deposition, the effective open areas 100 of the photo mask are attracted by magnetic plates (not shown) so that the effective open areas 100 are laid flat on a substrate to eliminate shadow effect. The sizes of the effective open areas 100 are arranged according to an effective area of the substrate (not shown). However, since the effective open areas 100 are provided with a plurality of vapor deposition apertures, the mass of an effective open area 100 and the mass of an ineffective area between two effective open areas 100 are different, whereby during the magnetic attraction of the photo mask, the sequences that the areas of different masses are attracted are different and this leads to that the effective open areas 100 may not be effectively laid flat on predetermined positions, resulting in positional shifts of pixels.